1179Chapter 32
Grounding and Interfacing
by Bill Whitlock
32.1 Introduction........................................................................... 1181
32.2 Basic Electronics....................................................................... 1181
32.2.1 Circuit Theory...................................................................... 1181
32.2.2 ac Circuits......................................................................... 1182
32.2.3 Capacitance, Inductance, and Impedance................................................. 1182
32.2.4 Single Wires....................................................................... 1183
32.2.5 Cables and Transmission Lines......................................................... 1184
32.3 Electronics of Interfaces................................................................. 1185
32.3.1 Balanced and Unbalanced Interfaces..................................................... 1185
32.3.2 Voltage Dividers and Impedance Matching............................................... 1186
32.3.3 Line Drivers and Cable Capacitance..................................................... 1187
32.3.4 Capacitive Coupling and Shielding...................................................... 1187
32.3.5 Inductive Coupling and Shielding....................................................... 1188
32.4 Grounding............................................................................ 1189
32.4.1 Earth Grounding.................................................................... 1190
32.4.2 Fault or Safety Grounding............................................................. 1190
32.4.3 Signal Grounding and EMC........................................................... 1192
32.4.4 Grounding and System Noise.......................................................... 1193
32.4.4.1 Power Line Noise............................................................... 1193
32.4.4.2 Parasitic Capacitances and Leakage Current Noise...................................... 1194
32.4.4.3 Parasitic Transformers and Inter-Outlet Ground Voltage Noise............................ 1 194
32.4.4.4 Ground Loops.................................................................. 1194
32.5 Interface Problems in Systems............................................................ 1195
32.5.1 Degraded Common-Mode Rejection..................................................... 1196
32.5.2 The Pin 1 Problem................................................................... 1198
32.5.3 Balanced Cable Issues................................................................ 1200
32.5.4 Coupling in Unbalanced Cables........................................................ 1202
32.5.5 Bandwidth and RF Interference......................................................... 1203
32.6 Solving Real-World System Problems...................................................... 1203
32.6.1 Noise Perspective................................................................... 1203
32.6.2 Troubleshooting..................................................................... 1204
32.6.2.1 Observations, Clues, and Diagrams.................................................. 1204
32.6.2.2 The Ground Dummy Procedure.................................................... 1204
32.6.2.2.1 For Unbalanced Interfaces........................................................... 1205
32.6.2.2.2 For Balanced Interfaces............................................................. 1206
32.6.3 Solving Interface Problems............................................................ 1207
32.6.3.1 Ground Isolators................................................................ 1207
32.6.3.2 Multiple Grounding.............................................................. 1207
32.6.3.3 Unbalanced to Balanced and Vice Versa.............................................. 1208